The present disclosure relates generally to the field of braking systems. More particularly, the present disclosure relates to contactor control, acknowledgment and/or monitoring methods and systems in vehicle braking systems.
Various vehicles utilize electric motors (e.g., traction motors, alternating current (AC) motors, direct current (DC) motors, etc.) to provide propulsion. Such vehicles include but are not limited to: locomotives, utility vehicles, trucks, busses, monorail vehicles, hybrid vehicles (including hybrid automobiles, trucks, sports utility vehicles, buses, etc.), construction equipment, mining equipment, etc. Vehicles that use electric motors for propulsion can also use an electric motor technique called retard braking to decelerate or retard the motion of the vehicle (brake the vehicle).
Retard braking draws power from the electric motor operating as a generator. The power drawn from the electric motor slows the electric motor which in turn slows the wheels or tracks of the vehicle. Retard braking reduces wear on friction-based braking systems. The power from the motor can be provided to batteries (e.g., in a regenerative braking system) or can be dissipated through resistive or other electrical elements.
In one particular application, super heavy duty trucks such as mining trucks include a retard brake pedal. When the retard brake pedal is engaged, an electronic control system for the vehicle determines the desired deceleration based upon certain factors such as, pedal position, load, speed, etc., and selectively closes electronics, such as, IGBTs, SCRs, electronic switches or contactors to appropriately draw power from the electric motor and brake the vehicle. Each of the switches are disposed in a bank including an energy dissipative network. The energy dissipative network can include electrical elements disposed between a power node and ground node of a direct current (DC) bus which supplies power to and receives power from the electric motor.
Generally, each contactor includes main contacts for its energy dissipative network and a set of auxiliary contacts that are used to control the main contacts and to provide feedback to a vehicle control circuit. The vehicle control circuit can determine which main contacts are closed and opened in response to signals from the auxiliary contacts.
According to one example, the main contacts which are generally normally open contacts are controlled by a control circuit which includes a resistor in series with a coil. Normally closed auxiliary contacts controlled by the coil bypass the resistor in an economizer circuit. The normally closed auxiliary contacts generally are used to reduce the time required to close the main contacts. Once the main contacts are closed (the coil is energized), the normally closed auxiliary contacts are opened and current to the coil is provided through the resistor.
The auxiliary contacts also generally include normally open contacts for providing feedback to the vehicle control circuit for the retard braking operation. In addition, the auxiliary contacts can include normally open contacts for providing fail safe operations. According to one fail safe operation, auxiliary contacts serve as an interlock to prevent closing of remaining main contacts if the main contacts are not closed in the bank that energizes a fan or blower motor for cooling the dissipative networks. The fan motor is generally powered by energy provided from the electric motor for efficiency.
In conventional retard braking systems, auxiliary contacts can be the subjected to dust, carbon monoxide and other contaminants which prevent the auxiliary contacts from opening and closing correctly. Improperly operating auxiliary contacts can result in a drive fault or a loss of retard braking for a short period of time (e.g., a second or less). Although the fault can be reset after the short period of time and retard braking can return to normal operation, the driver may be forced to use friction brakes which require maintenance after using them. In addition, the auxiliary contacts may suffer more permanent malfunctions due to contaminants and require replacement or repair.
Accordingly, there is a need for a system and method that improves contactor monitoring and/or control in a retard braking system. Further still, there is a need for a more reliable retard braking system and method. Yet further still, there is a need for control and/or monitoring circuitry that requires fewer or no auxiliary contacts. Yet further, there is a need for a monitor circuit that senses the number of retard braking contacts that are closed without using auxiliary contacts. Still further, there is a need for an economizer circuit that does not use auxiliary contacts. Even further, there is a need for lower cost, more reliable retard braking systems.
Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.